The invention relates to reformed gas generators in general and more particularly to an improved method of operating a reformed gas generator.
Such reformed gas generators in which evaporated or atomized liquid higher hydrocarbons are reacted at elevated temperature with an oxygen containing gas to form a gas mixture containing methane, carbon monoxide and/or hydrogen, wherein the reactants to be converted are heated, if desired, to an elevated input temperature before they are conducted into the reformed-gas generator are known. The throughput of the reactants is variable and the air number .lambda. of the gas containing the free oxygen is generally between 0.05 and 0.2.
In what are known as reformed gas generators, atomized, evaporated or vaporized liquid hydrocarbons are reacted with an oxygen containing gas at elevated temperature to form a fuel gas (reformed gas) containing carbon monoxide, methane and/or hydrogen. For instance, air, which contains the oxygen in free form, or exhaust gas which contains the oxygen in bound form (CO.sub.2 and H.sub.2 0). may be used as the oxygen containing gas. The reformed gas generated can be used as a synthesis gas or a reduction gas in metallurgical processes. In particular, it can be mixed with combustion air and serve as a fuel gas for burners and internal combustion engines. Whereas, with unpretreated liquid fuel the incomplete evaporation of the fuel and the nonuniform mixing with combustion air lead to incomplete combustion and to the emission of harmful substances, the reformed gas can be better mixed with the combustion air and be burned largely without residue. Since it also has a high octane number, the addition of antiknock agents to the fuel is not needed for operating internal combustion engines, so that the content of health injurious substances in the exhaust gas is further lowered.
The reaction of hydrocarbons with air is an exothermic partial oxidation with low air numbers. The air number .lambda. is understood here to be the ratio of the air used for the oxidation to the quantity of air which would be required for a stoichiometric combustion of the hydrocarbons. The air number is kept low so that as little chemical energy as possible is used in the conversion and the calorific value of the fuel gas is not substantially reduced. Bound oxygen e.g. exhaust gas, can also be used as the oxygen carrier, in which case, however, the hydrocarbon is reacted endothermically and heat must be supplied to the generator. This increases the calorific value of the fuel gas produced.
A difficulty arises in that the generated reformed gas at thermodynamic equilibrium contains the hydrocarbon in part in the form of soot and coking products. Such soot, however substantially degrades the combustion of the reformed gas and leads in addition, to clogging of lines and valves, especially when used in internal combustion engines.
Catalysts have already been developed which catalyze endothermic as well as exothermic conversion reactions and lead, under suitable laboratory conditions, to soot-free fuel gas. Such catalysts are described, for instance, in U.S. application Ser. No. 585,398 now U.S. Pat. No. 3,984,210.
In U.S. application Ser. No. 439,870 now abandoned in favor of U.S. application Ser. No. 633,609, now U.S. Pat. No. 4,121,542operating an internal combustion engine with a reformed gas generator is also described. A mixture of hydrocarbon containing fuel and a primary oxygen containing gas is converted into a fuel gas in the reformed gas generator. This fuel gas is then drawn, mixed with combustion air, into the combustion chambers of the internal combustion engine by the suction of the latter. The amount of the fuel conducted into the reformed gas generator is controlled approximately proportional to the respective demand of the internal combustion engine. Air can be used as the primary oxygen containing gas, the air number being between 0.05 and 0.5 and preferably not more than 0.2. The air can be replaced, however, entirely or partially, by exhaust gas. The reaction temperature at the catalysts of the reformed gas generator can then be controlled by controlling the mass ratio of the air to the exhaust gas, where a stronger exothermic reaction and thus a higher reaction temperature corresponds to a larger share of air. Provision is made for heating the reactants to be converted to an input temperature as high as possible before they are conducted into the reformed gas generator itself. The heat required therefor is transferred, by means of heat exchangers, from the hot exhaust gas of the internal combustion engine. This should permit an endothermic reation of the fuel with exhaust gas which is as far reaching as possible and which leads to a conversion of the waste heat of the exhaust gas into the chemical energy of the fuel gas.
According to the operating conditions of the reformed gas generator used, the quality of the reformed gas produced is different even if one and the same catalyst is used. If a mixture of hydrocarbons and air is fed into a reactor in such a manner that the input temperature of the mixture, the air number and the throughput are held constant or are varied only slowly, and if the reaction chamber is carefully heated to a constant temperature by supplying external heat, reformed gas without soot can be generated, and the degree of conversion of the hydrocarbons can be increased with increasing reaction temperature, increasing input temperature and dropping throughput practically up to complete conversion. In the method described in U.S. application Ser. No. 439,870 now abandoned in favor of U.S. application Ser. No. 633,609, however, the throughput varies rapidly in accordance with the demand of the internal combustion engine and a changing amount of hot fuel gas is presented to the heat exchangers which heat the reactants and the reaction chamber, and which have a certain intrinsic inertia. The input temperature of the reactants and the reaction temperature in the reaction chamber are thus subjected to rapid fluctuations. The quality of the reformed gas produced also differs accordingly and the generation of soot cannot be precluded or only precluded by a fast acting, elaborate control system.